This invention relates to a method of preparing a composite article, to a composite article formed thereby, and to an adhesive composition useful for forming such composite articles. In particular, the method of this invention includes forming an uncured assembly containing substrates and a homogeneous fluid and then exposing the assembly to polymerization conditions. Composite articles are prepared by bonding two or more substrates together with an interposed polymeric adhesive composition. The composite articles desirably have good adhesive strength; that is, the polymeric adhesive composition must adhere well to the substrates and be resistant to forces that lead to separation. Especially desirable are composite articles with good adhesive strength over a wide range of temperatures.
Some composite articles are made of relatively thin, flat layers; such composite articles are generally known as laminates. The method of this invention is useful for preparing various types of composite articles, including laminates, especially flexible laminates. Laminates are used to provide packaging which is light-weight and flexible. Typically, laminates are formed from combinations of various polymeric films, including, for example, polymeric substrates with low surface energies, bonded by a bonding composition to identical polymeric films, to different films, and/or to metal foils. It is desirable to use the bonding composition at a low application weight to minimize the weight of the laminate, to maintain flexibility, and to minimize cost.
New bonding methods are desired which allow the preparation of composite articles from opaque substrates. Multilayered composite articles are also desired which may be formed with a single cure step. One approach to these goals has been to bond the substrates with a bonding composition that is applied as a liquid and then exposed to elevated temperature or to radiation such as, for example, ultraviolet (uv) radiation or electron beam (e-beam) radiation. However, cure with uv radiation often requires the use of photoinitiators, and photoinitiators or the fragments of photoinitiators resulting from photolysis are generally low molecular weight materials which may adversely affect the properties of the composite article. Compositions that are curable by exposure to electron beam radiation generally do not require photoinitiators.
Adhesives cured by radiation have been disclosed by U.S. Pat. No. 5,747,551. However, such composite articles, while they often have good adhesive strength at room temperature, are known to lack good adhesive strength at elevated temperature. An object of the present invention is to provide composite articles with good adhesive strength at a wide range of temperatures.